Power harvesting for future gadgets?

Powering devices and gadgets of the future will be one challenge that offers plenty of opportunity for innovation.  Power harvesting from the kinetic action of people or objects moving, or natural so-called green options such as solar and wind generation offer some contribution.  One innovation I came across today is a combination of solar and power harvesting from the heat of the human body.  IMEC have come up with a system that can generate 1mW indoors and can be fitted to a headphone like wearable device.